So I'm currently working on a project where I need to find the frequencies for specific peaks in my FFT plot of an audio file. However, I'm not sure how to actually get the frequencies that correspond to the peaks I'm interested in.
This is my code: https://pastebin.com/zZW8B5Th
And this is a picture of my FFT plot: https://i.stack.imgur.com/jbqSx.jpg
Essentially, I'm trying to construct a Fourier Series from the signal. Although I know how to find the coefficients of the sine/cosine terms, I'm just a little confused on how to find the frequency.